In the past no satisfactory solution has been found for cooling said region by natural circulation of the water and of the emulsion of water and steam to be heated and vaporized. It has therefore been necessary to place tubes therein that are fed by means of forced circulation pumps drawing from tubes lining the vertical walls of the hearth via lengths that include portions extending downwards.
An object of the present invention is to provide apparatus for cooling such a natural circulation region by means of a system of continuous tubes including no portions extending downwards.